Skeletal System

SKELETAL SYSTEM ANATOMY

When a child is born, there are 270 bones that make up the human skeletal system. In an adult body, there are only 206. At any given time between birth and death, there can be a varying number of bones in the human body. The process of ossification alters the number of actual bones in the body. During adolescence and early adulthood, bones fuse together to create one bone and complete the growing process. Bones go through this process to allow for human growth and development. The term skeleton is translated from Greek, meaning “dried up.” Yet living bone it a living entity, changing, growing, rebuilding, and supporting life in more then the simple human ability to walk upright.

BONES

Bones are considered individual organs within the body structure, each with its own developmental role to play and each contributing to the body’s function on its own level. Bones are constantly growing, forming, reshaping, and healing without the body ever noticing the changes. As a natural response to injury, stress, or growth issues, small extra bones may form across pressure points of tendons as well as in the process of healing itself. In some cases, a bone may begin to heal itself and apply the system of regrowth, but cease to stop the regrowth process, which leads to the formation of additional bones or bony growths in the body. This type of bone growth is known as sesamoid bones.

The skull is made up of separate plates that fuse together during childhood. This plating of the skull is what allows women to bear children vaginally, the skull of an infant is born somewhat malleable yet with enough structure to protect the brain. A small percentage of adult bodies developed extra bones in the joint where the plates have fused in the skull. These extra bone growths are known as sutural, or wormian, bones.

Sesamoid bones and sutural bones are not necessarily definitive bones in every body. While kneecaps are an example of sesamoid bones that every body has not all human bodies have additional sesamoid or sutural bones.

The department of science which practices the study of bones is known as osteology, and has been responsible for research which has produced everything from which vitamins and mineral are necessary for healthy bone growth to the value of bone density and even the process of replacing bone with artificial materials.

The axial skeleton has two basic functions, one is to protect the internal parts of the body from damage and the other is to hold the human body upright and in its basic formation. The axial skeleton refers to the skeletal parts of the head, neck, and torso and includes specifically the skull, auditory ossicles, hyoid bone, vertebral column, and the ribcage.

The skull is probably the most recognizable of all bones, as it defines and holds the shape of the human head. The cranial bones create the smooth and rounded surface that was very obviously designed to protect the brain. The facial bones create the front features and are distinguishable by their obvious placement of the eyes, nose, and mouth. The facial bones create a supportive frame for the facial structure, as a deformity of the facial bones would lead to a deformity of the face.

The auditory ossicles are necessary for the human ear to hear sound. Their job is to transmit the vibration that is sound through the ear canal and through the central nerves of the ear and create “hearing.” These small but important bones are located on each sode of the human skull and are tucked into the middle ear chamber.

SKELETAL SYSTEM DIAGRAM

Image: Skeletal System

The hyoid bone is set firmly between the jawbone and the larynx and is responsible for the human ability to swallow as well as provides physical support to the tongue. This bone does not assist with the ability to speak, however s deformity of the hyoid bone can cause speech problems.

The vertebrate column is comprised of 26 bones segregated by small disks of cartilage to permit movement and flexibility. The “spine” is responsible housing the central nervous cord as well as holding the human body in an upright position. The core of the vertebrate column is comprised of fluid, nerves, and the body’s electrical system as it connects to the brain. The sacrum finishes off the vertebrate column with a few fused inflexible vertebrate which make up what is commonly called the tailbone and medical referred to as the coccyx. The coccyx and the sacrum in conjunction with the pelvic bone form a firm area in the middle of the body from which legs, torso, and abdomen meet and extend. This is considered the core of the body.

RIB CAGE

The rib cage is a combination of bone and cartilage that forms to create a protective barrier around a variety of inner organs, including the heart and the chest. The bones of the ribcage extend outward and around from the spinal column and create a “cage” which is attached to the sternum (the bone in the center of the chest which gives the ribcage grounding) via cartilage. The ribcage is responsible for protecting the inner organs of the chest wall along with giving the torso shape and depth. The ribcage holds 12 pairs of ribs of varying length and width.

The skeletal section which is comprised of the appendages is appropriately called the appendicular skeleton. This includes the appendages such as the bones of the arms, legs, and the bone structures which anchor them to the axial skeletal system.

The pectoral girdle is created by the bones of the shoulder blades and the collarbone, also known as the paired scapulae and the clavicles, respectively. The pectoral girdle is grounded to the axial skeleton via the sternum. Muscular systems which are responsible for creating movement of the arms are anchored to the pectoral girdle.

The upper extremities are made up of a series of bones which begin with the brachium, commonly called the arm. The arm is made up of two basic parts, the brachium and the antebrachium. The brachium is one solitary bone, the proximal humerus. The lower half, the antebrachium, is made of two basic bones, the ulna and the radius. Together, these three bones construct the arm from the shoulder to the wrist. Carpal bones, metacarpal bones, and a series of phalanges create the wrist to the fingertips.

The ossa coxae make up the majority of the pelvic girdle. The ossa coxae are commonly called the hip bones. The pelvic girdle houses the excretory system as well as the reproductive system and in women it can separate to allow for the birth of a baby. The pelvic girdle is anchored to the axial skeletal system via the sacrum. The syphysis pubis attaches the anterior portions of the ossa coxae together. The pelvic girdle is ingeniously designed to support the weight of the human body as well a protecting the organs and systems which fit snugly inside.

The lower extremities, which are commonly known as the legs, are made up of a similar structure to the upper extremities with different functions. The upper halves of the lower extremities are comprised of the proximal femur, also known as the thigh bones. The tibia and fibula create the lower half of the leg. The tibia is the common bone referred to as a shin bone. Tarsals, metatarsals, and phalanges are the bones which create the ankle and foot, completing the lower extremities. The purpose of these bones is to create a stable walking platform for the human body. Unlike the upper extremities, which create an elbow by the joining of the bones without protection, the lower extremities create a patellae or a knee cap to protect the knee joint.

SKELETAL SYSTEM FUNCTIONS

Bone is a particularly durable material, with intense strength and resistance to both wear and decay. The immense strength of bone is created by inorganic components and can last centuries under the appropriate conditions. Bone’s ability to be naturally preserved has allowed modern science to unearth the past and learn about life on earth all the way back to prehistoric times. Only preserved bone has allowed science a glimpse into the lives of humans before written history.

Bones are designed for numerous tasks within the human body. Besides the obvious functions of giving the human body its basic structure and providing protection for the soft materials of organs beneath, it is also responsible for storing fat in the medullary cavity, as well as storing minerals for healthy bodily functions and the production of hemopoiesis within the bone marrow.

Without the support provided by the skeletal structure, the human body would have no shape, no structure, and be a mass of skin, tissue, and organ that would not be able to perform independent movement. This support is the basis of human life. Despite the strength of bones, the weight of the organs, tissue, and muscles of an average sized human is about 5 times greater than the weight of the bones.

SKELETAL SYSTEM STRUCTURE

The skeletal structure is ingeniously designed to protect the most vulnerable of body parts. The skull protects the brain as the spinal column protects the spinal cord and thus the body’s central nervous system. The protection offered by the skeletal structure is extraordinarily important. Without the ribcage, the spleen, the heart, the lungs, the liver, and the great vessels would remain vulnerably exposed and a very simple accident would almost certainly mean death without this protection. The spongy bone tissue even subtly protects the blood production sites of the body.

Without the skeletal structure, the body’s muscles would have nothing to attach to, as the ligaments and tendons are anchored to the body’s bones. Without this system the body would not be able to perform basic bodily movements. The muscles which are attached to the bones via ligaments and tendons are able to lift that bone and manipulate it into a variety of positions, which creates movement.

The process of the creation of new blood cells is medically referred to as hemopoiesis. This process contributes new blood into the body’s supply at the rate of 2.5 million blood cells per second. Infant children, who lack the bone marrow necessary to contribute to this process, rely on the spleen and the liver for this process. The liver destroys blood cells as it cleanses the blood and purifies the blood stream, and of course these blood cells require replacement.

Lipid is a form of fat that is stored in the adipose tissue which is placed within the medullary cavity. This cavity is within the hollow portion of some bones, but not all. This intrinsic construction is known as yellow bone marrow.

Calcium and phosphorus comprise the inorganic matrix of bone. This mixture of precious mineral accounts for most of the weight of the bone, about two thirds, and is responsible for the strength and durability of the bone’s structure. In the human diet, about 95% of the ingested calcium and phosphorus are absorbed by the body’s bones and teeth. Without these minerals, muscles could not contract and blood would be unable to clot and cease excessive bleeding, and the passage of ions and nutrients between cell membranes would not happen. Phosphorus in its own is responsible for the nucleic acid activity of DNA, RNA, and ATP utilization. When the dietary demands of the body are not met, these minerals are extracted from the bones for the body’s use. While not as dramatically, the bone tissue also stores fluorine, magnesium, sodium, and strontium.

Like all of the body’s systems, the skeletal system is not an independent system. It relies upon the proper functioning of other systems in the body in order to operate properly, just as other systems within the body rely on the skeletal system to operate properly in order to reach maximum function potential. The skeletal system is necessary in its own right for its own primary purpose, but also is necessary to keep the rest of the body in full operative function.